US2027519A - Cold light source - Google Patents

Description

Jan. 14, 1936. J. B. DAVIS ET AL COLD LIGHT SOURCE Filed Sept. 24, 1932 Patented Jan. 14, 1936 s PATENT OFFICE COLD LIGHT SOURCE John Burgess Davis, Keyport', N. 1., and James L.

Simpson, New York, N. Y., assignors to Columbia Phonograph Company, Inc., Bridgeport, Conn., a corporation of New York Application September 24; 1932, Serial No. 634,643

'This invention relates to new and useful im- .-provements in lamps and has relation to a lamp particularly adapted for use in television apparatus. 5 An object of the invention is to provide a lamp which will give intense illumination.

Another object is to provide a lamp as stated and including means whereby the illumination from the lamp may be concentrated or confined 10 so as to form a small intense-spot of light.

A further object is to provide a lamp as stated and which is so constructed asto "deliver a cold li ht.

Other objects and advantages will become ap- ;5 .parent from a consideration of the following detailed description taken in connection with the accompanying drawing wherein satisfactory embodiments of the invention are shown.- However, it will be understood that the invention is m not limited to the details disclosed but includes all such variations and modifications as fall within the spiritof the invention and the scope of the appended claim.

.' In the drawing: v

151 Fig. 1 is a view partly in sectionand partly in side elevation showing a complete lamp constructed in accordance with the invention;

1 l ig. 2 is a somewhat similar Mew showing a slightly modified construction; y no Fig. 3 is a detail view showi g a slightly modifiedparrangement of fused silica cone arrangement which may be employed; and

4 Fig. 4 is a detail view of the coil.

vIt is well known that gas at low pressure in an 865 enclosed chamber when introduced into a radio frequency field may be made to ionize and resonate so as to emit light fiiciently in the visible and ultra-violet frequencies. The vapor of meronly has been demonstrated to be particularly.

so efilcient when used in this way, emitting about five candle-power for every watt of electrical energy dissipated in the vapor.

Referring now to the drawing and at first particularly to Fig. 1, the mercury is enclosed in a I 45 highly evacuated quartz bulb 5 including a body portion the walls of which are tapered as shown and at one endthe body 6 may include a hollow bulb like portion 1 while at its other end the body is enlarged 'as at 8 and closed as by a wall so or window 9. Leading from the lower side of the enlarged portion 8 of the bulb is a tubular portion in communicating at its lower end with a hollow bulb i l which bulb forms a reservoir and any contain mercury as indicated at It. so 'niceflectivendof thelamp orbulb lisrepresented by the fiat wall or window 9 which may be optically ground. A high frequency coil I3 is located closely adjacent this wall or surface and the energy dissipated is sufiicient' to evaporate a portion of the mercury and eneigize the vapor. 5 To facilitate this operation the coil may be carried about the chamber or reservoir H as indicated at ll. Any excess of mercury will condense in the chamber or bulb-like portion i and the intensity of the varying magnetic field in the 1d coil is suchas to maintain a suificiently high vapor pressure in the forward or enlarged portion 8 of the body 5.

When the body 6 is introduced into a magnetic field the energy dissipated in the body is much 16 'more than suflicient to excite the mercury vapor in the space just adjacent the flat surface l. Consequently with such an arrangement a large portion of the light produced or all the energy consumed, is not in a form readily available for so use. with the bulb entirely withdrawn from the coil and with the coil in close relation to the region adjacent the window or wall 8 the region in contact with said wall becomes more intensely excited-than if said wall or said region were as within the coil.

The coil l3 (see particularly Fig. 4) is in the form of a pancake coil arranged closely adjacent the end or wall 9 of the bulb 5 and the inner turn of the coil is just large enough for the bulb to 30.

pass through. Obviously, the coil may have a greater or lesser number of turns than is shown in the accompanying drawing. Further, the bulb ll may be heated either by stray field from the coil It or by continuing an additional turn of 5 the coil about the bulb as at ll.

The rapid movement of electrons and ions in the bulb 5 may prove a source of diiilculty in the higher candle power lamps in that the bombardment of the quartz or silica surface of the bulb 40 by the ions and electrons results in the generation of heat. This heat is enough to bring the silica to a bright red glow. In order to reduce the heating eflect of this bombardment we have arranged for cooling of the quartz surface. 45

To this end a water jacket l5, which is preferably of quartz fused to the body, is disposed chamber serves to equalize the water pressure when the water expands due to heating.

If desired, and to decrease the energy absorbed by the cooling water, water of the grade known as electrolytic conductivity water in a closed system wherein the water circulates primarily because of its own 'variation in density may be used. This conductivity water and in fact the water used in the system irrespective of the character of the water may be cooled as by enclosing the coil I I in a housing II and constantly passing water through said housing from any suitable source.

When, to a large extent, the ionization is conlined to the forward region of the bulb as the portion I in Fig. 1 a relatively large cooling chamber I! may be used and thus the necessity for conductivity water may be eliminated. This is to the fact that the stray field will not, of itself, be suiiicient to cause much heating of the water due to eddy currents.

In the device thus far described it will be appreciated that a high candle power is obtained at the end or window 0. In television, particularly, it is important to have not only high total candle power but high candle power intensity. For good scanning it is advisable to have a point source of light of high intensity. To this end a solid cone ll of transparent or translucent refractory material which does not conduct electricity, such as fused quartz, fused silica or the like, is employed with the bulb I.

The cone 2! may be formed with the bulb I or may be formed separate therefrom and sealed on the window or wall of the chamber or enlarged portion 8 of the bulb and the light from said wall of the bulb is thus concentrated down to a window 22 whose surface is optically smooth and whose diameter does not exceed of an inch. When the cone is formed mte from the bulb and sealed on the window I the large end of the cone as well as the window is ground optically smooth. As at prwent determined the length of the cone must be at least four or five times the diameter of the window or wall I. The slope of the coneissuchasto insurethatmost of the light emanating from the window I strikes the cone surface at less than the critical angle of reflection. In this way almost 100% concentration of light is attained.

Light emanating from the window 22 spreads over a complete hemi-spherical surface and in order to pick up this light and concentrate it we have the choice either of lenses or of mirrors. If lenses corrected for spherical aberration are used, evidently a large portion of the total 180' sphericalanglewillnotbeintercephd. Ifparabolic mirrors are used for pick-up it h evident tlnt the radio frequency coil will cast a large shadow in the beam reflected from the surface of such mirror.

.To carry the light away from the coil or to a point where the light reflected by a. parabolic mirror will not be partly intercepted by the coil a cone 24 such as shown in Fig. 3 may be employed. In this figure the end of the cone is turned downwardly as at 25 and the small window is indicated at 20. Of course, if desired, the extended portion represented at 28 may be in the form of a suitably tapered rod sealed to an end surface of the cone and the rod may be bent in the desired manner.

In Fig. 2 is shown a slightly modified arrangement of lamp. In this figure all of the parts are of the same construction and bear the same reference characters as the parts shown in Fig. 1 with the exception that a tube 21 is provided connecting the bulb or chamber 1 with the reservoir I i. whereby mercury condensed in the bulb l is continuously returned to the reservoir, the said mercury returning through the tube 21. If desired, the cone 24 of Fig. 3 may, of course, be applied to a lamp having a body structure including tube 21 as disclosed in Fig. 2. Also, it will be understood that the complete cooling system as shown in Fig. 1 may be applied to the arrangement shown in Fig. 2, but a part of the cooling system being shown in that figure to prevent needless repetition.

It will now be understood that with the lamp as described with the coil ll located closely adjacent the window or end wall 9 the most intense ionization will take place adJacent said wall with the result that the energy expended is more nearly all consumed in useful work. Further, it will be understood that the cone need not be formed with the body 8 but may be formed separate therefrom and sealed thereto in position over the wall or window 8. Also, the inclined walls of the body I serve to return the condensed mercury to the reservoir.

Having thus described the invention, what is claimed is:

A mercury vapor induction lamp comprising an evacuated container, said container having a discharge region and mercury storage region, a quantity of mercury in said storage region, a water cooling jacket for said discharge region, and high frequency means disposed in proximity tosaid storage and discharge regionsfor providing a supply of mercury vapor and maintaining a discharge therethrough.

JAMEL. N. I

J. Bumms DAVIS.

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